The present invention relates to a handbrake setting unit for setting the handbrakes of road vehicles, such as cars. The invention relates principally, but not exclusively, to the setting of handbrakes on the production assembly line of such vehicles and it will therefore be convenient to describe the invention in relation to that application. However the invention is not restricted to such use and could have other applications, such as for resetting the handbrake if the handbrake cable is replaced, or disassembled or requires further adjustment.
It is a problem with the handbrake or bowden cable of many new vehicles, that they require slack adjustment of the handbrake cable relatively soon after the vehicle is placed on the road. Slack in the handbrake cable occurs principally due to bedding and seating of components of the handbrake upon initial use of thereof, while cable stretching also contributes to the slack generated.
The tensioning of a handbrake cable on a production line to operating tension is known as xe2x80x9chandbrake settingxe2x80x9d and it would be preferable if the handbrake setting procedure was such as to avoid the need for early handbrake adjustment. This is desirable, because the requirement for early adjustment of the handbrake is not only inconvenient, but because most vehicle manufacturers provide free of charge at least the first post sale scheduled service, the cost of resetting the handbrake is normally a cost which must be absorbed by the manufacturer. Due to the high volume of vehicles requiring resetting, some manufacturers are therefore exposed to a significant and wasteful expense.
It has been found that applying a load to the handbrake cable of an assembled handbrake in the production line has benefit in bedding and seating the components of the handbrake. It has therefore been known to apply a tensile load to the handbrake cable during setting and in one form, the load has been applied to the handbrake cable through the handbrake adjuster nut. The handbrake is positioned in the applied position and a torque driver, fitted with a socket is positioned onto the handbrake adjuster nut. The driver is activated to rotate in a clockwise direction which in turn revolves the socket and the adjuster nut. In this method, the nut sits on the handbrake and it can therefore not move down the adjuster thread. As the nut is turned, the handbrake adjuster rises through the nut and as a result, tension increases within the handbrake cable. Consequently, the torque required to rotate the adjuster nut increases as tension in the handbrake cable increases. The torque driver stops rotating when the torque required to rotate the adjuster nut rises to that of the predetermined torque driver setting. This torque driver method, uses the adjuster nut to apply and maintain the tensile load applied to the handbrake cable. In practice, the load generated by the torque driver can vary with variation in the interference between the nut and the adjuster thread and that can result in a substantial variation from the load required to be applied to the cable. In particular, the load can be below that which is required. This process has thus been found to be very inconsistent and therefore has not found wide use.
It is an object of the present invention to overcome or at least alleviate the disadvantages of the prior art. It is a further object of the invention to provide a method of setting a handbrake such as to significantly delay the need for hand-brake adjustment when use of the handbrake commences. It is still a further object of the invention to provide a method by which the components of a handbrake assembly can be caused to substantially fully bed and seat during installation or setting of the handbrake. It is another object of the invention to provide a device for setting a handbrake to achieve one or more of the above mentioned objects.
According to the present invention there is provided method of setting the handbrake cable of an automotive handbrake, said handbrake cable including a threaded member fixed at one end and a nut threaded onto said member and in the set condition of the handbrake said nut engaging against a seat to maintain tension in said handbrake cable, said method including gripping said threaded member and retracting said member to apply a tensile bedding load to said cable, which bedding load exceeds the required set load of the cable in the set condition, returning said threaded member from the retracted position to reduce the tensile load on said cable to said set load, rotating said nut down said threaded member to engage said seat and releasing said threaded member.
The method of the invention advantageously causes the handbrake components to bed and the cable to stretch during the cyclic load to a significantly greater and more consistent extent compared with the methods for setting handbrakes, so that the slack generated in the handbrake during early use of the vehicle is significantly reduced and the period by which an adjustment setting is required is, as a consequence, extended.
The invention is particularly more beneficial than the torque drive method described earlier, in that the invention applies and releases cyclically, a dedicated load prior to setting, and that cyclic load application causes the handbrake components to bed and the cable to stretch. In contrast, the torque driver method applies a single load once during setting and the bedding and stretching benefits are negligible or at least very limited. However, that basically is the only known system, and it has continued to be used by some manufacturers in the absence of an alternative solution.
For convenience, hereinafter, the load applied to the handbrake cable will be referred to as the xe2x80x9cbedding loadxe2x80x9d. The bedding load is applied at least twice, although preferably it is applied and released, or xe2x80x9ccycledxe2x80x9d, a plurality of times and the number of applications will depend on the characteristics of the handbrake being set. It is preferable that at least four bedding load cycles be applied to the handbrake, although additional cycles, taking the total number to perhaps six or eight, could equally be applied. Generally, the limiting factor in relation to the number of applied cycles, is the time allowable for such a procedure in the production line. It is envisaged that a cycle time of approximately 10-15 seconds will typically be available, to apply the bedding load or cycled bedding loads of the invention.
Preferably the bedding load applied to the handbrake cable exceeds the operating tensile load that would normally be applied to the cable under ordinary operating conditions of the handbrake. Preferably the bedding load exceeds the ordinary operating load by a reasonable amount in order to realise the advantages of the invention and preferably the difference between the bedding and the ordinary operating loads is in the order of approximately 100%, although the load should not exceed the designed abuse load of the handbrake system. In theory, a sufficiently large bedding load could bed, seat, compress and stretch all the relevant components of the handbrake sufficiently to extend the first service interval of the handbrake to a period equal to subsequent service intervals.
The difference between the bedding load and the ordinary operating load may be subject to the number of cycles applied to the handbrake, such that with a greater number of cycles, the bedding load could be reduced. However it must be appreciated that a limitless number of light loads will not, for example, pre-stretch the handbrake cable beyond a certain length. The only way that can be done is to apply a greater load. Conversely, a higher bedding load may require a reduced number of cycles to achieve the same level of handbrake bedding.
The method of the invention can be carried out in any suitable manner, and in one embodiment, the method involves gripping the handbrake cable with gripping means at, or in the region of the cable adjuster thread, and retracting the gripping means to apply a tensile bedding load to the cable. The load can be released by releasing the gripping means from the cable, but in a preferred manner, the gripping means remains in gripping engagement with the cable and is returned from the retracted position to release or substantially reduce the bedding load. Advantageously, the gripping means may grip the handbrake cable by threadably engaging the adjuster thread.
The invention further extends a device for setting the handbrake cable of an automotive handbrake, said handbrake cable including a threaded member fixed at one end and a nut threaded onto said member and in the set condition of the handbrake said nut engaging against a seat to maintain tension in said handbrake cable, said device including gripping means to grip said threaded member and retracting means to retract said gripping means to a retracted position to apply a tensile bedding load to said cable which bedding load exceeds the required set load of the cable in the set condition, return means to return said threaded member from said retracted position to reduce the tensile load on said cable to said set load, rotating means to rotate said nut down said threaded member to engage said seat whereafter said gripping means is arranged to release said threaded member.
Preferably the gripping means includes a threaded portion, such as a sleeve or recess for threadably engaging the adjuster thread. Preferably the threaded portion is rotatable so that it can be threaded on to the adjustor thread and preferably the device includes drive means operable to rotatably drive the threaded portion into threaded engagement with the adjuster thread. In one form of the invention, the drive means is operable to drive a socket member which houses the threaded portion. In this form of the invention, the drive means preferably is reversible to allow the threaded portion to be driven on to and off the adjuster thread. The drive means preferably is electric or pneumatic, although other types of drive could also be adopted.
The gripping means can be retracted to apply a tensile bedding load to the handbrake cable in any suitable manner and in one form of the device of the invention, the retracting means includes a piston/cylinder arrangement. A single piston within a cylinder can be employed for this purpose although in a preferred arrangement, a pair of pistons which are connected in series are employed to increase the output of the retracting means. The retracting means could alternatively be an electric motor and rack. Advantageously in either arrangement, the device can be assembled as a hand-held device and still provide the load output required.
In an arrangement which employs retracting means having a piston or pistons, the threaded portion can be connected to a drawbar extending from the or one of the pistons and retracting movement of the threaded portion occurs upon retracting movement of the or each piston. In such an arrangement, movement of the piston(s) in the reverse direction causes the threaded portion to return partially or fully from the retracted position. Alternative means to return the threaded portion from the retracted position could however, be employed.
Preferably drive of the threaded portion can be controlled automatically, so that when the adjuster thread is properly engaged by the threaded portion, drive thereof is discontinued. Sensing means can be adopted for this purpose and in one arrangement, the depth of threaded engagement of the adjustable thread by the threaded portion is sensed. That sensing means operates when the device is first applied to the adjustable thread and preferably it controls the drive means that drives the socket, so that upon full threaded engagement between the threaded portion and adjuster thread, the drive means is temporarily de-activated.
Sensing means can also be applied to the piston movement to sense the value of the load being applied, along with the period for which the load is applied. The sensing means could be optical sensors, strain gauges, timers etc.
Rotation of the threaded portion can also be controlled by the use of a drive arrangement which employs a splined section of the socket member to selectively drive a drive member. The drive member has a section, preferably a head at one end thereof, which is configured, preferably hexagonally, for engagement by the splined section and that engagement preferably is dependent on the position of the drive member relative to the socket member. Thus, when the head section is engaged within the splined section, rotation of the socket member causes resultant rotation of the drive member. When the drive member is shifted to disengage the head section from the splined section, rotation of the socket member will cause no rotation of the drive member. The drive member is arranged to selectively, as described above, drive the threaded portion. The threaded portion may be integrally formed as part of the drive member, but preferably it is separately formed and includes engagement means for engaging the drive member. For example, the drive member may include a blade for engagement within a slotted end of the threaded position. That arrangement may permit drive member and the threaded portion to be shifted axially relative to one another, but to rotate together upon rotation of the drive member by the socket member.
The above described arrangement enables the threaded portion to be rotated as necessary, but by displacement of the drive member from engagement with the splined section of the socket, the socket can still be rotated without rotating the threaded portion. This arrangement can be employed advantageously to lower the adjuster nut after the bedding cycle has been completed and the handbrake load is being set. In this arrangement, means are provided to rotate the adjuster nut simultaneously with socket rotation, and in a preferred arrangement the internal splined surface of the socket member engages the head of the nut for rotation thereof. In this arrangement, in one direction of socket rotation, the adjuster thread can be engaged by the threaded portion and the bedding load cycle can then be applied, drawing the adjuster thread and the adjuster nut into the socket and away from the seated position of the nut. When the bedding cycle is complete and the setting load is to be applied, the adjuster thread and nut will remain in, or will again be drawn into the socket, but to a lesser extent than under the bedding load. The nut will therefore be raised away from its seat and rotation of the socket can be employed to run the nut down the adjuster thread until it is seated without simultaneously rotating the adjuster thread, which would otherwise cause the adjuster thread to be drawn further into the threaded portion until it engaged the closed end thereof, whereafter continued rotation of the adjuster thread could damage the drawbar assembly. The use of the drive arrangement to control rotation of the threaded portion allows for the prevention of such relative movement.
It is preferred that the device of the invention be hand-held for hand operation and the device therefore preferably includes a hand grip. In a preferred embodiment, the drive means is contained within the handgrip and a housing defining the cylinder containing the piston(s) in attached thereto. A casing preferably extends from a forward end of the housing and encloses the socket and related components, such as the gripping means. In this arrangement, the drive means preferably drives the socket through a drive train. The handgrip is preferably offset from perpendicular to the housing by approximately 15 degrees.